1. Field of the Invention
The present invention relates to a method of protecting part of a coastline against erosion, by placing in a wave breaking zone, a device to dampen water flow generated by the breaking waves.
The invention also relates to an arrangement for protecting a part of a coastline against erosion. The arrangement includes a device being placed in a wave breaking zone and adapted to dampen water flow generated by the breaking waves.
In a zone where the water is so shallow that waves have an influence on the sea bed, sea-bed material will be suspended by waves and transported inwards and outwards perpendicular to the coastline, this material settling at roughly the same rate as it was suspended, thereby leaving the coastline more or less intact. However, the water flow will often have a flow component along the coastline. Such a flow component occurs when waves are angled to the coastline in the breaking zone. This results in sand and other erosion material/beach and coast material being moved along the coastline. Sand that is washed away along the coast from one place to another is not always replaced to the same extent from a part of the coast located upstream. Thus, sandy beach can be washed away or built-up and extended even in the case of relatively small changes in the direction of the incoming waves at the part of the coast in question. This phenomenon whereby a sand beach is washed away and re-built can be amplified by general water flows in the coast region.
Such coast erosion is a well known problem and proposed solutions include the use of beach facings, wave breakers, groynes, artificial reefs, pneumatic wave dampers, artificial "seaweed" (bottom-secured oil-filled hoses) among other things.
One problem with these known solutions, however, is that they are very expensive to construct and are either built to provide the intended function for a specific predominant wave direction or to dampen incoming waves. None of the solutions is aimed at actively influencing the coast-parallel net loss of sediment along a heavily eroded coast section.
In reality, however, wave direction varies in a manner that cannot be fully anticipated, and consequently fixed structures along the coastline can sometimes give a less desirable result.